Comparison
235/55 R18 vs 255/45 R18
255/45 R18 is a lower-profile take on 235/55 R18 — same 18-inch wheel, shorter sidewall. This setup moves rolling diameter well outside the usual OEM tolerance.
The speedometer error is noticeable and may warrant a recalibration if you rely on indicated speed. Less sidewall flex usually translates to crisper turn-in and a slightly stiffer ride over rough pavement. More tread on the ground tends to improve dry grip and stance, with a small fuel-economy and clearance tradeoff. The 3–5% diameter gap puts this in caution territory: doable on many cars, but verify clearance and consider recalibration.
TakeSuits drivers who value sharper steering and appearance over outright ride softness.
Quick math: 255/45 R18 is 29.0 mm shorter than 235/55 R18, shifting the speedometer by -4.05%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
-29.0 mm
-4.05%
Speedometer at 100
95.9 km/h
-4.05% error
Ground clearance
-14.5 mm
ride height delta
Sidewall change
-14.5 mm
revs/km: 463.5
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/compare/235-55-r18-vs-255-45-r18Detailed comparison
| Metric | 235/55 R18 | 255/45 R18 | Difference |
|---|---|---|---|
| Overall diameter | 715.7 mm | 686.7 mm | -29.0 mm (-4.05%) |
| Sidewall height | 129.3 mm | 114.8 mm | -14.5 mm |
| Circumference | 2.248 m | 2.157 m | -91.1 mm |
| Revs / km | 444.8 | 463.5 | +18.8 |
| Ground clearance | reference | -14.5 mm | -14.5 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 95.9 km/h | -4.05 km/h |
Verdict: warning
Between 3% and 5% — noticeable speedometer drift; recalibration may be advisable.
Speedometer impact
At a true 100 km/h, your dashboard will read 95.9 km/h after switching to 255/45 R18 — a -4.05% offset. Use the speedometer error calculator to recheck for other indicated speeds, and the speedometer error guide for the full background.
Ground clearance change
The new tire's half-diameter changes ride height by -14.5 mm. Small differences are absorbed by suspension travel, but anything beyond ±10 mm can affect headlight aim, fender clearance and bump-stop margin. See the plus-sizing guide before committing.
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235/55 R18
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255/45 R18
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